My above mentioned patent application sets forth compounds which retard the hardening of phenolic resole resins admixed with hardening quantities of lightburned magnesium oxide or magnesium hydroxide, either alone or together with an ester functional hardening agent. Table 3 in the above mentioned patent application also relates to retarding the hardening of periclase in admixture with a phenolic resole and an ester functional hardening agent by use of a retarder.
This invention relates to methods and compositions useful in the manufacture and use of ceramic and refractory compositions. More particularly this invention relates to methods and compositions for retarding the hardening of compositions containing hardburned magnesia or deadburned magnesia, both of which are simply referred to herein as "magnesia aggregate", and a curable phenolic resin, with or without the inclusion of an ester functional hardening agent. Such retardation is accomplished by incorporating in the compositions certain compounds such as those which supply 2- or 4-acetylphenol, also referred to as 2'- or 4'-hydroxyacetophenone, tetraalkoxy silanes, or fluoride, bifluoride, malate, tartrate, citrate, phosphonate, or phosphate anions to the composition.
Phenolic resins are widely used as refractory binders. However, they have certain drawbacks when used as binders for magnesia aggregate. Mixtures of magnesia aggregate and a hardenable or curable phenolic resin are relatively inactive in comparison with mixtures of lightburned magnesium oxide and phenolic resole resins. However, when magnesia aggregate is mixed with liquid phenolic resins, the wet mixtures tend to harden in a comparatively short time at ambient temperature. This reduces the time that the mix can be retained before it must be used such as shaped into various articles. The addition of a retarder of this invention prolongs the working time of such mixtures by retarding their rate of ambient temperature hardening.